Apparatus and circuit for telephone-switchboards.



Nu, 669,545. Patented Mar. I2, I91".

F. a. McB'ERTY. APPARATUS AND i'Jll'w'GUl'l' FOR TELEPHONE SWITGHBOARDS.

(A nmim filed June 12, 1889.)

(No Model.)

waifle s as Tu; NORRIS Perms c0 morouruou WASHINGTON, o. c.

UNlTE FRANK R. MOBERTY, OF EVANSTON, ILLINOIS, ASSIGNOR TO THE WESTERN ELECTRIC COMPANY, OF CHICAGO, ILLINOIS.

APPARATUS AND CIRCUIT FOR TELEPHONE-SWITCHBOARDS.

SPECIFICATION forming part of Letters Patent No. 669,545, dated March 12, 1901.

Application filed June 12,1899.

T wZZ whom, it may amt/earn:

Be it known that I, FRANK R: MOBERTY, a citizen of the United States, residing at Evanston, in the county of Cook and State of Illi-' nois, have invented a certain new and useful Improvement in Apparatus and Circuits for Telephone-Switchboards, (Case No. 75,) of which the following is a full, clear, concise, and exact description.

This invention applies to telephone-switchboards wherein lines are united through the medium of repeating-coils; and it consists in means for avoiding cross-talk in the cables of the switchboard, while maintaining the static :5 balance of the lines to prevent inductive disturbances in the lines.

I11 telephone-switchboards wherein both grounded and metallic circuits center, which must be connected with each other indis- 2o criminately by means of the switching apparatus of the board, it has been the universal practice to provide for each grounded line a wire extending throughout the switchboardcable as a .mate to the grounded-line wire,

groundedat one or two points in the switchboard, in order that a grounded line might act as a metallic line with relation to adjacent circuits, especially when connected with a metallic circuit. This practice has been main- 0 tained in switchboards of the common battery type, in which the link conductors are provided with an interposed repeating-coil with a ground at its center, and in order that the grounded idle wire of the grounded circuit might not impair transmission through the medium of the repeating-coil by forming a closed circuit about one winding in inductive relation to the windings active in trans mitting the telephonic current the seriallyconnected windings of the repeating-coil in each through-conductor of the line-circuit have been placed together on a single core, which was, in effect, isolated from the core wherein the serially-connected windings of the other line conductor were included. l/Vhile this construction has secured a high degree of efficiency in telephonic transmission under the various conditions, it has been defective in causing cross-talk in the cables of the switchboard and in disturbing the balanced condition of metallic circuits, so that Serial No. 720,175. \N0 modeln such circuits exposed to external inductive influences became noisy, inasmuch as one winding of the repeating-coil associated with one limb of the metallic circuit'was characterized by a variable impedance dependent on the nature of the telephone-line with which the metallic circuit was associated.

The present invention consists generally in the association with a grounded line or an unmated line conductor carrying telephonic current of an open conductor near to and parallel therewith and a repeating-coil having inductively-related windings in the idle wire and the line, respectively, whereby when telephonic currents are traversing the line-wire equal but oppositely-directed variations of potential are produced in the idle parallel wire, which neutralize the inductive effect of the line-wire on adjacent circuits.

In a more specific form in adaptation to the conditions of the common battery switchboard the invention consists in the usein each link-conductor for uniting lines of a repeating-coil with four windings of substantially equal resistance and in like relation to the core of the repeating-coil and in inductive relation to each other and in an open mate wire for the grounded line, with which one grounded winding of the repeating-coil is associated during connection with such lines.

The invention is illustrated in simple form in the attached drawing. This figure represents, diagrammatically, a metallic-circuit telephone-line united with a grounded-circuit telephone-line through the agency of linkconductors with an interposed repeating-coil and bridged supply-battery.

Line conductors 1 and 2 form a metallic circuit extending to station a and terminating within the switchboard in the contact-pieces of a spring-jack b. Those portions of the metallic circuit which lie within the cabling in the switchboard, which may be two hundred feet in length, are represented as lying 5 near together. They are, in fact, twisted together to constitute a pair devoid of induction upon adjacent circuits. The wire 3 is the line conductor of the grounded line extending to station a. It likewise terminates in a spring-jackb' in the switchboard. Within the switchboard-cable it is mated with a wire 4, which terminates in an open end at the main distributing-board or other terminal point of the switchboard-cable and is connected with that contact-piece of the springjack with which the return line conductor of a metallic circuit would be connected.

The like contact-pieces of the spring-jacks are united through the link conductors 5 and 6, whose terminal plugs are inserted in the spring-jacks. Each conductor 5 and 6 of the plug-circuit includes two serially-connectedwindings of a repeating-coil at, these windings being designated d (1 01 61 respectively. The points of junction of the serially-connected windings are united by a grounded bridge, in which a source of current 6, as a storage battery, is placed. The windings d d and d 61 should preferably be of equal resistance and in like inductive relation to the iron core. This condition may be obtained by constructing the windings as four helices, each of two parallel wires, each helix being equal in length to half the core and connecting the Wires of the inner winding at one end of the core with the wires of the outer winding at the other end of the core after the manner described in Patent No. 382,856 to John A. Barrett, dated May 15, 1888.

If two metallic circuits be united by means of the link conductors 5 6, provided with such a repeating-coil, obviously the static balanc ing of both metallic circuits will be maintained, so that external inductive disturbances will produce no troublesome sounds in either. Likewise when a metallic circuit is united with a grounded line, as shown in the drawings the balance of the metallic circuit 1 2 is not disturbed, since both windings d and d are in like inductive relation to the windings d and d which are associated with the grounded line 3 4. Transmission is not impaired by the presence of winding since this winding is in an open circuit. Moreover, each variation of telephonic current in the circuit produces a corresponding opposite variation of the potential in the mate wire 4 of the grounded line 3, which neutralizes any inductive action which the wire 3 tends to exert on neighboring circuits, and thus maintains freedom from cross-talk in the cable containing the wire 3 4. Likewise if two grounded circuits be connected together transmission between the stations of the lines is not impaired by closed circuits in inductive relation to the active windings of the repeatingcoil, while the static inductive eitect of impulses in each line is counterbalanced by variations of potential induced in the mate wire of the line by the winding of the repeating-coil associated with it.

I claim as new 1. The combination withanumber of telephone-circuit conductors, of a single telephone line-wire adjacent thereto, aconductor constituting a mate wire for said single line conductor, and forming a twisted pair therewith, and an appliance inductively connecting the two wires of the pair, whereby the inductive eifect of variations of potential in the single telephone line-wire upon neighboring telephone-circuits is neutralized, as set forth.

2. In combination, grounded telephonelines in a switchboard-cable, a mate wire for each line-wire forming a twisted pair therewith, a repeating-coil having a winding in the line conductor and a winding in said mate wire, the circuit of the mate wire including said winding being open at one terminal and grounded at the terminal of the winding, as described.

3. The combination inaswitchboard wherein metallic circuits and grounded lines center, the wires of said circuits being formed into cablos,of open mate wires for the grounded lines terminating in the spring-jacks of the lines, link conductors for uniting lines, and repeating-coils i n-the link conductors, each repeating-coil having four windings in substantially like inductive relation to each other, one terminal of each of said windings being grounded and the other terminal being associated with the link conductor to be brought into connection with one of the linewires or mate wires of a line; whereby the static balance of metallic circuits is maintained, while cross-talk in the switchboard is prevented, as described.

4. The combination with a single line conductor carrying varying current, of an open conductor near to and substantially parallel therewith, and an inductive appliance uniting said conductors and permitting the passage of varying currents between them, but not permitting the passage of direct current, whereby the static inductive effect of variations of potential in the current-carrying wire is neutralized by the opposite variations in the mate wire, as described.

In witness whereof I hereunto subscribe my name this 6th day of June A. D., 1899.

FRANK R. MO BERTY.

Witnesses:

ELLA EDLER, DUNCAN E. WILLETT. 

